Creatviity versus Productivity-Medical fiction- royalty versus self-publishing

What happens when one has to depend on their writing to financially support themselves. If you don't produce you can't pay the electric bill or put food on the table. Then the creativity becomes the same as the productivity.
Does that change the creative process? Does it sharpen or undermine it?
If we speak of medical fiction, I suppose you can artificially classify writers into those whom have worked professionally in the field and those that have not.
We like to think of clinically accuracy in medical fiction, (see previous posts), so therefore someone that has not worked in the field would have to do some research, or there is also those whom have had experience as a patient, or what we sadly refer to now as a CONSUMER of health care.
So then we have the medical professional who pays the bills via their day job. They write because they need or want to write. Complete creativity, or maybe obsessive need to be heard or tell the story.
Then there are the writers who pay their bills via writing and they happen to have a medical degree of some sort. Some of them worked in the field for years, some have a degree and residency training but never did much work in the field. Most don't see patients too often anymore, receive advances and are compensated by big royalty publishing houses. They are under contract to produce. Many of the other medical fiction writers dream of this. But on the other hand they can create from the heart, they don't have to produce work that must sell in mass market. That pressure is not there. There are more medical people writing than ever, especially with the proliferation of kindle and nook etc as well as the mainstreaming of small presses and real self-publishing.
All the self-publishing options give free will and avoid any "suck-up sell out" mentality of the author for the work, of course that leads to a lot of self-published literary garbage. (don't quit your day job kind of stuff) On the other hand if the writing is "good enough"  which means marketable to be picked up by royalty publisher and agent etc, the author may have to submit to lots of changes to make the book even "more marketable".
I suppose the few medical fiction writers achieving "celebrity" status have the best of all worlds, although I am  not sure they don't struggle with the issue of being true to thyself, in other words do they write from the heart or do they just "create" what the editor demands?